The present invention relates to the technical area of pyrotechnic charge firing devices of the fuse plug type, notably for hand grenades, that include a pyrotechnic circuit detonated conventionally by a firing pin operated by the movement of a handle associated with a cotter pin.
This firing device must meet the requirements of safety, reliability and low production cost. In particular, for safety during storage and transit, the pyrotechnic train must be configured so that it can be disabled.
This device must also allow the user to select one of the following three firing modes for the pyrotechnic charge: delay, impact mode, or an impact-delay mode.
It must be possible for all the component parts to be manufactured using an automated production process. Their assembly should permit the use of robotic production equipment. In this technical field a number of designs have been proposed.
French Patent FR 2.517.048 discloses a fuse plug for a hand grenade having three modes of operation with storage and operational safeties that interrupt the pyrotechnic train and lock the firing pins. This plug has two pyrotechnic trains having one part in common, one train being related to one firing pin specifically for delayed operation and the other train working with a second firing pin specifically for impact operation. The grenade operating mode is selected using an outer ring fitted with a stud against which a plate turns under rotary motion from a timer. This plate also determines the alignment of the pyrotechnic train which results after the cotter pin is removed and a delay is determined by the timer.
This fuse plug has several disadvantages. In particular, it incorporates two principal non-aligned firing pins that collaborate with two pyrotechnic trains, leading to complex manufacture and operation.
Another disadvantage lies in the fact that the alignment of the pyrotechnic train and the arming of the operating modes both depend on a timer, which can have an adverse effect on safety and on the functional reliability of such a fuse plug. A fire, kinetic energy impact or nearby explosion can lead to the accidental ejection of the cotter pin followed by rotation of the plate, leading to an irreversible alignment of the pyrotechnic train.
In addition, the impact-delay function is equivalent to self-destruction of the grenade in the absence of percussion, and not to a delay function triggered by the impact function.
French Patent FR 2.458.790 discloses a multi-purpose fuse plug with a throwing safety. This plug, which is very similar to that described in the previous patent, can operate in four different ways, and includes two independent, principal firing pins each corresponding to different modes of operation, and a selector having two rotating discs controlled by a timer movement in storage and operation of the throwing safety. This fuse plug also includes an impact detector coupled to one of the firing pins which is configured in an armed position directly after release of the handle, which necessitates the throwing safety.
Most of the disadvantages mentioned above are also found here. Notably, the use of a timer mechanism, which may become faulty, to control the alignment of the pyrotechnic train, as well as to ensure ignition safety, is disadvantageous.
With regard to the impact-delay mode, the delay function is not triggered by the impact function.
French Patent FR 2.682.471 also discloses a storage safety for a fuse plug that interrupts the pyrotechnic train. This interruption is obtained by a pivoting element with a radial orifice positioned between a delay module and a primer composition. Rotation of this part, caused indirectly by the release of the handle, automatically aligns the pyrotechnic train.
French Patent FR 2.465.189 also shows a fuse plug for a grenade that includes a pyrotechnic train interrupted by a rotating device operated by a delay mechanism involving the release of glass beads, which allows definitive alignment of the train after a predetermined time interval following initiation of the train.
The operating principle of the pyrotechnic train interruptions described in these two patents and in the patents mentioned earlier have the major drawback of resulting in an automatic and irreversible alignment of the train during storage in a hostile environment.
Moreover, if any single component essential to locking should fail, which could, for example, occur by accident with no persons present (due to fire, explosion or impact), the firing procedure is inevitably initiated.